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Old 05-04-2010, 12:32 AM   #11 (permalink)
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I wonder if there is any difference in gains between a longbed and shortbed with a cover like this.
The long bed truck would stand to gain more from an aerodynamic cover than a short bed if I am not mistaken. This is due to the fact that the air has more chance to get caught in the box and hit the tailgate rather than flow past the cab and over the tailgate. There are gains to be made in both cases however. I have a short bed as you can see.

It's too soon to post results yet, but my first run in very windy and cold conditions were netting me almost the same mpg's as I was getting in warm relatively calm weather.

More results to come......

Swede

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Old 05-04-2010, 04:35 AM   #12 (permalink)
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Light weight, and looks great, I'll give it two thumbs up
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Old 05-04-2010, 08:55 AM   #13 (permalink)
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Side hinge ??

Swede, I've been hoping to build a similar cover for my truck. My thought was to hinge it on the driver's side, and open from the passenger side. That way, the weight will be on the bed, not up near the roof line, and I believe it will be a much easier build. Also, if you ever go to a rear camera, wiring along that side will be simple too.

I hope if/when I ge around to building my cap it comes out as nice as yours.
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Old 05-04-2010, 10:07 AM   #14 (permalink)
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Quote:
Originally Posted by swede View Post
The only challenge will be figuring out how to prevent the bottom front edge from hitting the box rails due to the lower swept arc as the lid opens. I'll have to think up some fancy hinge geometry for that I guess.
As long as the pivot point of the hinge is lined up with or in front of the front edge and at the top of the cover, I think it will be physically impossible for it to hit the bed rails or the cab.
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Old 05-04-2010, 12:59 PM   #15 (permalink)
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Originally Posted by bikin' Ed View Post
Swede, I've been hoping to build a similar cover for my truck. My thought was to hinge it on the driver's side, and open from the passenger side. That way, the weight will be on the bed, not up near the roof line, and I believe it will be a much easier build. Also, if you ever go to a rear camera, wiring along that side will be simple too.

I hope if/when I ge around to building my cap it comes out as nice as yours.
Thanks for the compliment. The important thing to remember is to use light wieght materials. I doubt that I will have any issues with an upper hinge as the cap is less than 30 lbs. That's probably less than the hatch on a metro!!

I find that the huge Dumbo ear mirrors on the truck, while creating drag, do give an excellent veiw to the rear. I havent missed the rearview mirror that much yet, but then again I'm not the type to use it much anyway

Swede
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Old 05-04-2010, 05:10 PM   #16 (permalink)
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Lid

Swede,Sorry! This is my first look at your project.
I like what you're doing.From an airflow standpoint the only hitch I might think of,is how the sides 'tumble' aggressively from the cab back,falling at an ever steeper angle in such a short distance to the back.
Tuft-testing will reveal if flow is good there.Hope so.
Otherwise,you should be rewarded for your efforts at the pump.Nice work!
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Old 05-04-2010, 06:55 PM   #17 (permalink)
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Thanks for the comment aerohead.

The first real highway run I did was this weekend and I had no way to see air flow over the top of the lid but the drivers side I could see out of my side mirror. I attatched tufts and observed the air flow that followed the contour from the b pillar of the cab and around the leading edge of the cap. I observed a little flow disturbance right at that edge and as the air continued along the cap it had a definite upward flow toward the top of the cap. I'm not sure if this is normal or even desirable on an aerodynamic cap like this. The other factor that may have skewed any real flow observations is the fact that I had a 90 degree crosswind coming from the passenger side of the truck during my drive.

I know that the angle looks steep but when measured from the beginning of the curve to the end at the tailgate with and angle meter, I have 11 degrees of slope. This is well within acceptable limits from what I understand.

The radius of the angle change from the top plane of the cab roof to the slope may be a little on the steep side but tuft testing with a chase/observation vehicle will tell.

One Question:

When tuft testing, are the tufts supposed to flow straight back with no movement along the surface of the substrate, or do they sometimes move side to side along the surface while still laying parallel to the substrate?
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Old 05-04-2010, 07:00 PM   #18 (permalink)
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tufts

Quote:
Originally Posted by swede View Post
Thanks for the comment aerohead.

The first real highway run I did was this weekend and I had no way to see air flow over the top of the lid but the drivers side I could see out of my side mirror. I attatched tufts and observed the air flow that followed the contour from the b pillar of the cab and around the leading edge of the cap. I observed a little flow disturbance right at that edge and as the air continued along the cap it had a definite upward flow toward the top of the cap. I'm not sure if this is normal or even desirable on an aerodynamic cap like this. The other factor that may have skewed any real flow observations is the fact that I had a 90 degree crosswind coming from the passenger side of the truck during my drive.

I know that the angle looks steep but when measured from the beginning of the curve to the end at the tailgate with and angle meter, I have 11 degrees of slope. This is well within acceptable limits from what I understand.

The radius of the angle change from the top plane of the cab roof to the slope may be a little on the steep side but tuft testing with a chase/observation vehicle will tell.

One Question:

When tuft testing, are the tufts supposed to flow straight back with no movement along the surface of the substrate, or do they sometimes move side to side along the surface while still laying parallel to the substrate?
Swede,thanks for the heads up.Sounds like she's okay! The pressure is lower on top so the side tufts will be attempting to 'go' there,As long as they are not oscillating wildly from side to side you should be in the money!
Dr. Kamm's car did the same thing.
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Old 05-04-2010, 07:03 PM   #19 (permalink)
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On a side note....

Unfortunately I am a smoker, but it can lead to some interesting observations. When I used to toss a butt out the window, (I don't do it often) I would notice the wind grab it and wildly toss it around right out of the window. Now I tossed one out and it flew smoothly along the side of the truck and dropped down to the rear smoothly in the trailing wake. A huge difference in the smoothness of the airflow along the side and into the trailing wake seems to be the answer to that.

What do you all think?
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Old 05-04-2010, 07:10 PM   #20 (permalink)
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Not being seasoned like the others, sounds like you did something right.

Do you hear less wind turbulance at speed?

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I think you missed the point I was trying to make, which is that it's not rational to do either speed or fuel economy mods for economic reasons. You do it as a form of recreation, for the fun and for the challenge.
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